1. Field of the Invention
The present invention relates to a solid-state imaging device, a driving method thereof, and an imaging system.
2. Description of the Related Art
The speed of light is 3×108 m/s. Since this is known, a distance to an object can be measured by emitting a light pulse towards the object from a light source, receiving reflected light that is reflected from the object, and measuring the delay time of the light pulse. The TOF (Time-Of-Flight) method is a method for measuring the distance to an object by measuring the flight time of the light pulse. A distance measurement range with respect to a delay time measurement range can be read and, for example, and if an apparatus were available for which the delay time measurement range is 1 μs and the delay time measurement resolution is 1 ns, then a 150 m range could be measured with a 15 cm resolution, and the apparatus could be used as an on-board distance sensor for vehicles.
Technology has been proposed that acquires a two-dimensional image for ranging by applying this principle to a solid-state imaging device. Japanese Patent Application Laid-Open No. 2004-294420 discusses technology that uses a CMOS-type solid-state imaging device that has a pixel configuration according to a charge sorting method.
A signal component corresponding to a precedent portion of a reflection light pulse that arrives after a delay when an irradiation light pulse is reflected from an object and a signal component corresponding to a following portion thereof are sorted by a switch. By detecting these signals for each pixel to determine a ratio between the precedent portion and the following portion, distance information can be obtained for each pixel.
Further, Japanese Patent Application Laid-Open No. 2004-045304 discusses technology that uses the TOF method for a common CCD-type solid-state imaging device.
According to a solid-state imaging device that employs TOF according to a charge sorting method, at least two memory components are required in a single pixel, and the sensitivity is prone to decrease because the aperture ratio of the photodiode cannot be increased. Thus, if the pixel size is increased, it is difficult to provide a large number of pixels. Consequently, there is the problem that it is difficult to also use the device as a common multi-pixel solid-state imaging device.
Further, when applying the TOF method to a common CCD-type solid-state imaging device, there is the problem that because delay components of reflected light are detected in frame units, it is difficult to obtain an image for ranging at a high speed.